An electrically-operated window lift is known from German Patent Publication DE 12 44 610, which allows lowering the window of a motor vehicle along a curved track. In the process, guide rollers disposed in the vicinity of the area of lower corners of the window engage a profiled section of guide rails which are associated with them. A further, third guide rail is located in the central area of the door and supports a toothed rack which is in engagement with teeth of a power take-off pinion of a motor-gear unit. The third guide rail is also curved, therefore, the motor-gear unit must perform a translatory movement along the lower edge of the window during raising and lowering of window. The translatory movement of the motor-gear unit is assured by means of a slide rail connected with the lower edge of the window.
With its three guide rails and the sliding rail for the motor-gear unit, the described window lift has a relatively elaborate design. In addition, the construction of the center guide rail having the toothed rack on one leg of the profiled section and the sliding edge on the other leg of the profiled section is not very well suited for efficient production. During inclement weather there is a large chance of icing of the slide rail supporting the motor-gear unit, which could prevent the operation of the window.
German Patent Publication DE 19 26 800 describes a window lift device having a toothed rack drive, wherein the toothed rack is guided in a profiled window guidance section. In this case, the toothed rack is preferably embodied in one piece with the guide rail. This very simple design integrates the tasks of force transmission and window guidance in only one component, because of which a high degree of compactness is attained, along with the use of only a few individual parts. However, its disadvantage lies in that the position of the drive which is fixedly connected with the frame and cannot be freely selected. The connection of a drive pinion with tooth elements of the toothed rack must always be disposed closely below the door cavity which, however, when an electrical drive is used, quickly leads to problems because of the reduced availability of space at this location. In addition, the proposed solution is not suitable in connection with windows without a lateral frame which can house the toothed rack.
German Patent Publication DE 40 26 214 A1 and European Patent Publication EP 0 490 341 A1 describe operating devices which employ spindles, which also permit a compact design. The poor efficiency of spindle drives must be considered disadvantageous. If strongly curved windows are used, it is necessary to employ expensive flexionally elastic spindles. The noise problems connected with spindle drives are often hard to overcome, because the spindle itself cannot perform any guidance tasks.
A further window lift system with a motor seated at the lower edge of the window and a drive rod disposed obliquely in the door is disclosed by Japanese Patent Publication JP 4-155 083A. The power supply is shown to be a screw-shaped cable extending from the motor into a lower corner area of the door. In the course of the movement of the window between its upper and lower stops, the cable crosses a large section of the door area, so that a relatively large space must be kept free for the cable. In addition, it is possible that, when the door is slammed shut, undesirable noises are caused by the unfastened sections of the cable.
It is, therefore, the object of the invention to develop an electrically-operated displacement device for windows or sliding roofs of motor vehicles, employing a toothed rack drive system and guidance system, which is distinguished by a high degree of compactness and by cost-effective manufacture, which can be easily adapted to the various requirements of different door configurations. It is desired that the device be formed from a small number of individual parts. It is also desired that guidance system employed by such device not reduce the free space required for other components, such as speakers or the like.